INSE^CTIVOROUS PLANTS. 153 



Desiring to obtain conclusive evidence for his claim, Vines undertook further researches. His 

 former methods were unavailing in that he was unable to separate leucin or tyrosin in measurable 

 quantities. His results, obtained by another method, he considers convincing. He says : 



"Tiedemann and Gmelin observed in 1831 that on the addition of chlorine water to the liquid 

 resulting from a pancreatic (tryptic) digestion, after acidification, the liquid acquires a color varying 

 from pink to violet; when concentrated there is a violet precipitate. This coloration is due to the 

 presence of a substance which, together with leucin, tyrosin, and other bodies, is a product of tryptic, 

 as distinguished from peptic proteolysis. The substance in question is a chromogen termed proteinochro- 

 mogen by Stadelmann, but better known by the name, tryptophan, given to it by Neumeister, and 

 its presence affords a ready means of distinguishing tryptic from peptic digestions." 



Vines's experiments using this method with the liquid from somewhat prolonged digestion of 

 fibrin by pitcher liquid of Nepenthes in the presence of either hydrochloric or citric acid, gave the 

 tryptophan reaction. He also obtained this reaction in liquids resulting from the digestion of fibrin 

 by both pineapple juice and papain. These produce leucin and tyrosin in larger quantities than does 

 pitcher liquid. There was no evidence of bacterial putrefaction, the products of which also have 

 been found to contain tryptophan, i.e., there was no odor of indol or scatol. 



The action of nepenthin, as Vines calls this enzym, was also tested on albumoses and peptones, 

 with the result that the digested liquid gave the tryptophan reaction. Pineapple juice and papain 

 thus tested reacted similarly. Controls of various sorts gave negative results. 



Hence Vines concludes that the three enzymes, nepenthin, bromelin, and papain, have essentially 

 the same proteolytic action, which is tryptic. Nepenthin, however, acts only in acid liquids, while 

 bromelin and papain are most active in neutral liquids. Trypsin acts most readily in alkaline 

 liquids. According to their mode of action, however, they may be grouped with trypsin. Vines 

 thinks, also, that these investigations strengthen his suggestion that all known proteolytic enzymes 

 of plants are tryptic. 



Bacteria in Hop Glands. 



In 1892, Mohl attributed the formation of lupulin in hops to the presence of a Micro- 

 coccus, called by him M. humuli Launensis. The organism is said to be present in enormous 

 numbers in the glands of the living hop plant. Apparently no cultures were made, only 

 microscopic examinations. No conclusive evidence was advanced. After reading his 

 paper and especially after studying the glands of the hop-strobile one is prepared to appre- 

 ciate Braungart's comment: "Sonderbarer Bemerkung." The glands are full of oil drops 

 and of minute granules, some of which have an active Brownian movement when examined 

 in water but do not stain like bacteria. The latter are probably what Mohl saw. 



Bacteria with Algae. 



Kozzowitsch in 1892 to 1894 obtained marked increase of nitrogen in mixed cultures 

 of algae and bacteria, but no increase in pure cultures of the algae. He assumed, therefore, 

 that the algae and the nitrogen-fixing bacteria stood in a symbiotic relation to each other, 

 the bacteria obtaining their carbon food from the algae. 



In 1900 Kriiger und Schneidewind studied pure cultures of various lower algae on a 

 variety of culture media with and without combined nitrogen, and reached the conclusion 

 that these algae were unable to obtain their nitrogen from the air. Their paper does not 

 deal directly with the question of the relation of these algae to the nitrogen-fixing bacteria 

 of the soil. 



In 1903, Reinke published a paper on the symbosis of Volvox and Azotobacter, in 

 which he presented additional evidence in favor of the theory that Azotobacter furnishes 

 nitrogenous compounds to fresh water algae, as well as to the salt-water forms, with which 

 it is associated, and to the outer membranes of which it adheres closely ("so fest eingenistet 

 sind, dass ein Zellenverband von gewebeanlicher Innigkeit entsteht.") 



At his request Keutner made a large number of cultures of fresh water algae from the 

 plankton of Lankener Sea near Preetz, as well as from the ponds of the botanical garden. 

 The cultures, left to themselves during the summer vacation, showed in October a great 

 development of Azotobacter, and had furnished in the 200 cc. of nitrogen-free nutrient 

 solution an appreciable amount of combined nitrogen, on an average, about i mg. 



As an example of these experiments the culture of Volvox is given in detail. 



